What is static friction?
static friction is a force that resists the movement of two objects against each other when objects are initially at rest. A simple example is the wooden block sitting on the ramp - it is necessary to use the force to allow the block to slip on the ramp. Another term, kinetic friction, refers to the power that opposes objects that are already moving against each other. The power of these forces can be calculated and is known as friction coefficient. In real -life situations, static friction coefficient is almost always considered larger than kinetic but in carefully controlled experiments, where the surfaces of the objects have been thoroughly cleaned are generally the same. After a certain point, however, the object begins to move and at this point of friction, the force Will drop is necessary to move the object. For example, the friction force may correspond to the applied force up to 50 Newtons - the force is measured in Newtons (N) - but then it can drop to 40 N. Therefore, a force of over 50 N is required to achieve the movement of the object.>
Calculation of coefficient
Statical coefficients of friction can be calculated for any solid material or a few materials. The value of the coefficient may therefore apply to wood for wood, steel on steel or steel on wood. One way of calculating the value for a few materials is to place a block of one material on the ramp made of another - for one material would be a block and a ramp made of the same fabric. The inclination on the ramp gradually increases until the block slips down. The angle at which this happens can then be MyED to calculate the coefficient of static friction.
coefficient, if used in samples and equations, has a symbol μ - Greek letter MU. The index is usually used to distinguish the following two: μ s indicates static friction, while μ k means kinetic friction. For example, μ s for steel is 0.74, while μ k for this material is 0.57. This throwThe notes are for typical situations in real life and may vary a bit depending on the circumstances. Since the value of μ s may be affected by surface irregularities, impurities and traces of other substances, the value of μ k is considered more accurate and is usually stated when a simple coefficient of friction is required.
Factors affecting friction
A number of factors contribute to static friction, but usually the roughness of surfaces is the most important. Even if it has become smooth, otherwise the materials will vary in terms of fine detail of their surfaces. From a practical point of view, no surface is completely smooth, but some will have more irregularities than others. The difference is obvious in some cases: for example, a silk leaf has a very smooth texture that creates less friction, while the dry asphalt road is coarse and creates more resistance to movement. Other factors include electrostatic attraction and types of weak chemical bonds that can make upIT between surfaces.Examples
Many people are familiar with static friction because they encounter it almost daily; For example, it's at work when someone slips a book over the table. Initially, a small amount of force should be developed to move the book, but as soon as it moves, it will enter the game of kinetic friction and less effort will be required to move it. The amount of force required may vary according to circumstances. For example, if the book has a library cover and was wet, the book Wet will require more strength to move, while a brand new paperback book could easily slide over a dry wooden table with a faulty surface.
tables of static and kinetic friction coefficients are available for many common materials and their combinations. A higher value indicates greater friction, so more force should be used to cause movement. For example, μ s for aluminum on aluminum is 1.05 - 1.35, which is very high, while the value for polytetrafluorethylene (PTFE) on PTFE is 0,04, which is very low and makes it very slippery. It is difficult to push the stopped car in motion due to deliberate friction between tires and earth; This allows the controller more control and causes the car to be less likely to slip.
Calculation of brake distance
One examples of static friction application is to calculate the distance breaking for the car at a given speed and especially the conditions. Under normal circumstances, when the tires rotate on the road, it is static, rather than kinetic friction. Μ s for a dry tire on a dry road is about 1.00, while the value for a wet tire on the wet road is only 0.2 - that is, the breaking distance will be five times larger in wet conditions. In dry conditions, the car has 31 miles per hour (50 km / h), a brake distance of 33 feet (10 meters), while under wet conditions the brake distance of 164 feet (50 meters) would be. When tires move rather than rolling, along the surface - as wouldIt could have been in ice conditions - it is important kinetic friction.